Tutorial 4 — Electrochemistry

Note: This tutorial PDF consists primarily of scanned images. The questions below are reconstructed based on typical FAD1018 Tutorial 4 content on Electrochemistry.

Learning Outcomes

Understand redox reactions and electrochemical cells
Calculate cell potentials using standard reduction potentials
Apply Nernst equation
Understand electrolysis and Faraday's laws
Calculate Gibbs free energy from cell potential

Part A: Electrochemical Cells

Question 1

Consider the galvanic cell: $$Zn(s) | Zn^{2+}(1.0\ M) || Cu^{2+}(1.0\ M) | Cu(s)$$

Given: $E°{Zn^{2+}/Zn} = -0.76$ V, $E°{Cu^{2+}/Cu} = +0.34$ V

a) Identify the anode and cathode.

b) Write the half-reactions at each electrode.

c) Calculate the standard cell potential $E°_{cell}$.

d) Write the overall cell reaction.

e) Indicate the direction of electron flow in the external circuit.

Question 2

a) For the cell in Question 1, calculate the equilibrium constant $K$ at 25°C.

b) Calculate $\Delta G°$ for the reaction.

c) Is this reaction spontaneous under standard conditions? Explain.

Part B: Nernst Equation

Question 3

For the cell: $Zn(s) | Zn^{2+}(0.10\ M) || Ag^+(0.50\ M) | Ag(s)$

Given: $E°_{Ag^+/Ag} = +0.80$ V

a) Write the Nernst equation for this cell.

b) Calculate the cell potential $E_{cell}$ at 25°C.

c) Calculate the cell potential when $[Zn^{2+}] = 1.0$ M and $[Ag^+] = 1.0 \times 10^{-5}$ M.

Question 4

A concentration cell consists of two hydrogen electrodes: $$Pt | H_2(1\ atm) | H^+(?\ M) || H^+(1.0\ M) | H_2(1\ atm) | Pt$$

The measured cell potential is 0.118 V at 25°C. Calculate the unknown hydrogen ion concentration.

Part C: Electrolysis

Question 5

An aqueous solution of CuSO₄ is electrolyzed using inert electrodes.

a) Write the half-reactions occurring at the anode and cathode.

b) How many grams of copper will be deposited when a current of 2.0 A is passed for 30 minutes?

c) What volume of gas (at STP) is evolved at the anode during this time?

Question 6

a) State Faraday's laws of electrolysis.

b) A current of 3.5 A is passed through molten Al₂O₃ for 2 hours. Calculate:

The mass of aluminum produced
The charge passed through the cell

Part D: Applications

Question 7

a) Explain how a lead-acid battery works during discharge and recharge.

b) Write the overall reaction for a lead-acid battery.

c) Why do car batteries sometimes fail in cold weather?

Question 8

a) Describe the structure and operation of a fuel cell.

b) What are the advantages of fuel cells over conventional batteries?

c) Write the half-reactions for a hydrogen-oxygen fuel cell in acidic medium.

Key Concepts

Galvanic Cell — Electrochemical cell that produces electrical energy
Electrolytic Cell — Electrochemical cell that uses electrical energy
Standard Reduction Potential — Potential of half-reaction under standard conditions
Nernst Equation — Relates cell potential to concentration
Faraday's Laws — Laws relating charge to amount of substance electrolyzed

FAD1018 Tutorial 4 — Electrochemistry